1. Field of the Invention
The present invention relates to a hydrophilic treatment method and to a wiring pattern forming method.
2. Description of the Related Art
As illustrated in FIG. 1(a), when a wiring board is manufactured, first, a mask layer 14 made of a resin is formed on a metallic film 12, which is formed on the entire surface of one side of a resin substrate 10. Subsequently, patterning is performed on the mask layer 14. Thus, groove portions 16, 16, . . . from which the metallic film 12 is exposed, are formed in a bottom surface according to a wiring pattern to be formed.
Subsequently, as illustrated in FIG. 1(b), wiring patterns 18, 18, . . . are formed by filling each of the groove portions 16, 16, . . . with metal through electrolytic plating using the metallic film 12 as an electric power supplying layer.
Thereafter, as illustrated in FIGS. 1(c) and 1(d), the wiring patterns 18, 18, . . . having desired shapes are formed on the resin substrate 10 by removing the mask layer 14 to thereby remove the exposed metallic film 12.
However, the electrolytic plating using the metallic film 12 may cause air bubbles to adhere to the inner side surface of each of the groove portions 16, 16, . . . , which is formed by the mask layer 14, when filled with metal. When electrolytic plating is performed in a state in which such bubbles adhere thereto, the groove portions 16 are filled with metal in a state in which bubbles 100, 100, . . . adhere thereto, as illustrated in FIG. 2(a). Thus, the wiring patterns 18 are finally formed so that holes 102, 102, . . . are formed therein, as illustrated in FIG. 2(b).
The more easily the wiring patterns 18, in which the holes 102, 102, . . . , are formed due to the adhesion of the bubbles 100, 100, . . . are formed, the finer the wiring patterns 18 become.
Additionally, the finer the wiring patterns 18 become, the larger the proportion of the holes 102, 102, . . . , which are formed due to the adhesion of the bubbles 100, 100, . . . , to the wiring patterns 100, 100, . . . becomes. Thus, the strength of the wires reduces. Consequently, there is a fear of breaking the wire due to stress applied to the wiring pattern 18 in the subsequent step. Even when the wire is not broken, the values of electric characteristics, such as impedance, of the wiring patterns 18 become different from preset values thereof.
Meanwhile, one of the reasons for the adhesion of bubbles to the inner side surfaces of each of the groove portions 16, which are constituted by that of the mask layer 14, at the time of filling each of the groove portions 16, 16, . . . with metal by the electrolytic plating using the metallic film 12 as the power supplying layer is that the inner peripheral surface of each of the groove portion 16 is contaminated by performing patterning on the mask layer 14 and so forth.
Such a stain can be removed therefrom by dipping the resin substrate 10 into a weakly alkaline solution or an alcoholic solution and by performing a degreasing treatment thereon. However, this degreasing treatment promotes the peeling-off of the mask layer 14.
Thus, it has been studied to perform a plasma treatment on the resin substrate 10 to be electrolytic-plated, as proposed in JP-A-2000-127407 (Second Embodiment) which is hereinafter referred as Patent Document 1.
The stain on the inner peripheral surface of each of the groove portions 16, which is caused by the patterning or the like of the mask layer 14, can be removed by performing a plasma treatment on the resin substrate 10 to be electrolytic-plated, as proposed in the Patent Document 1. Further, an adhesion force acting between the mask layer 14 and the metallic film 12 can be enhanced when the electrolytic plating is performed.
However, although this reduces the possibility of occurrence of the phenomenon in which bubbles adhere to the inner side surface of each of the groove portions 16, which is constituted by the mask layer 14, during the electrolytic plating using the metallic film 12 as the power supplying layer, it has been found that this phenomenon still occurs.
According to the present inventor's study of such a phenomenon, the wettability of the inner side surface of each of the groove portions 16, which is constituted by the mask layer 14, with an electrolytic plating solution is insufficient. Thus, when the bubbles 100, 100, . . . mixed in the electrolytic plating solution adhere to the inner surface of each of the groove portions 16, the electrolytic plating is continued in a state in which the bubbles 100, 100, . . . adhere thereto.
Therefore, it is demanded to enhance the wettability of the inner side surface of each of the groove portions 16, which is constituted by the mask layer 14, with the electrolytic plating solution by performing a plasma treatment.
Incidentally, this enhancement of the wettability of the surface with the electrolytic plating solution can be regarded as equivalent to that of the wettability thereof with water, because most of the electrolytic plating solution is constituted by water.
Further, it is economical to form the metallic film 12 on the entire surface of one side of the resin substrate 10 shown in FIG. 1(a) by performing electroless plating. However, when the metallic film 12 is formed by the electroless plating, it is necessary to enhance the wettability of the resin substrate 10 with an electroless plating solution by dipping the resin substrate 10 into a weakly alkaline solution or an alcoholic solution and by performing a degreasing treatment thereon.
However, because it becomes a problem how to treat such a degreased solution, it is also demanded to enhance the wettability of the resin substrate 10 substantially without using the solution. This enhancement of the wettability of the resin substrate with the electroless plating solution can be also regarded as equivalent to that of the wettability thereof with water, because most of the electroless plating solution is constituted by water.